When logging into the application, the browser (Firefox) asks the user if they would like to save username and password. This is due to the username/password fields allowing autocomplete.
Login fields should have the autocomplete attribute disabled so that the username and password does not cache the credentials. In addition with autocomplete disabled the browser will not ask to store the credentials. E.g. “autocomplete=false”. Autocomplete can be disabled on individual input fields or for the entire form. Note that if autocomplete is not set, it defaults to true.